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package java.security.spec;

import java.math.BigInteger;
import java.security.spec.MGF1ParameterSpec;

/**
 * This class specifies a parameter spec for RSA-PSS signature scheme,
 * as defined in the
 * <a href="http://www.ietf.org/rfc/rfc3447.txt">PKCS#1 v2.1</a>
 * standard.
 *
 * <p>Its ASN.1 definition in PKCS#1 standard is described below:
 * <pre>
 * RSASSA-PSS-params ::= SEQUENCE {
 *   hashAlgorithm      [0] OAEP-PSSDigestAlgorithms  DEFAULT sha1,
 *   maskGenAlgorithm   [1] PKCS1MGFAlgorithms  DEFAULT mgf1SHA1,
 *   saltLength         [2] INTEGER  DEFAULT 20,
 *   trailerField       [3] INTEGER  DEFAULT 1
 * }
 * </pre>
 * where
 * <pre>
 * OAEP-PSSDigestAlgorithms    ALGORITHM-IDENTIFIER ::= {
 *   { OID id-sha1 PARAMETERS NULL   }|
 *   { OID id-sha224 PARAMETERS NULL   }|
 *   { OID id-sha256 PARAMETERS NULL }|
 *   { OID id-sha384 PARAMETERS NULL }|
 *   { OID id-sha512 PARAMETERS NULL },
 *   ...  -- Allows for future expansion --
 * }
 *
 * PKCS1MGFAlgorithms    ALGORITHM-IDENTIFIER ::= {
 *   { OID id-mgf1 PARAMETERS OAEP-PSSDigestAlgorithms },
 *   ...  -- Allows for future expansion --
 * }
 * </pre>
 * <p>Note: the PSSParameterSpec.DEFAULT uses the following:
 * message digest  -- "SHA-1"
 * mask generation function (mgf) -- "MGF1"
 * parameters for mgf -- MGF1ParameterSpec.SHA1
 * SaltLength   -- 20
 * TrailerField -- 1
 *
 * @author Valerie Peng
 * @see MGF1ParameterSpec
 * @see AlgorithmParameterSpec
 * @see java.security.Signature
 * @since 1.4
 */

public class PSSParameterSpec implements AlgorithmParameterSpec {

  private String mdName = "SHA-1";
  private String mgfName = "MGF1";
  private AlgorithmParameterSpec mgfSpec = MGF1ParameterSpec.SHA1;
  private int saltLen = 20;
  private int trailerField = 1;

  /**
   * The PSS parameter set with all default values.
   *
   * @since 1.5
   */
  public static final PSSParameterSpec DEFAULT = new PSSParameterSpec();

  /**
   * Constructs a new {@code PSSParameterSpec} as defined in
   * the PKCS #1 standard using the default values.
   */
  private PSSParameterSpec() {
  }

  /**
   * Creates a new {@code PSSParameterSpec} as defined in
   * the PKCS #1 standard using the specified message digest,
   * mask generation function, parameters for mask generation
   * function, salt length, and trailer field values.
   *
   * @param mdName the algorithm name of the hash function.
   * @param mgfName the algorithm name of the mask generation function.
   * @param mgfSpec the parameters for the mask generation function. If null is specified, null will
   * be returned by getMGFParameters().
   * @param saltLen the length of salt.
   * @param trailerField the value of the trailer field.
   * @throws NullPointerException if {@code mdName}, or {@code mgfName} is null.
   * @throws IllegalArgumentException if {@code saltLen} or {@code trailerField} is less than 0.
   * @since 1.5
   */
  public PSSParameterSpec(String mdName, String mgfName,
      AlgorithmParameterSpec mgfSpec,
      int saltLen, int trailerField) {
    if (mdName == null) {
      throw new NullPointerException("digest algorithm is null");
    }
    if (mgfName == null) {
      throw new NullPointerException("mask generation function " +
          "algorithm is null");
    }
    if (saltLen < 0) {
      throw new IllegalArgumentException("negative saltLen value: " +
          saltLen);
    }
    if (trailerField < 0) {
      throw new IllegalArgumentException("negative trailerField: " +
          trailerField);
    }
    this.mdName = mdName;
    this.mgfName = mgfName;
    this.mgfSpec = mgfSpec;
    this.saltLen = saltLen;
    this.trailerField = trailerField;
  }

  /**
   * Creates a new {@code PSSParameterSpec}
   * using the specified salt length and other default values as
   * defined in PKCS#1.
   *
   * @param saltLen the length of salt in bits to be used in PKCS#1 PSS encoding.
   * @throws IllegalArgumentException if {@code saltLen} is less than 0.
   */
  public PSSParameterSpec(int saltLen) {
    if (saltLen < 0) {
      throw new IllegalArgumentException("negative saltLen value: " +
          saltLen);
    }
    this.saltLen = saltLen;
  }

  /**
   * Returns the message digest algorithm name.
   *
   * @return the message digest algorithm name.
   * @since 1.5
   */
  public String getDigestAlgorithm() {
    return mdName;
  }

  /**
   * Returns the mask generation function algorithm name.
   *
   * @return the mask generation function algorithm name.
   * @since 1.5
   */
  public String getMGFAlgorithm() {
    return mgfName;
  }

  /**
   * Returns the parameters for the mask generation function.
   *
   * @return the parameters for the mask generation function.
   * @since 1.5
   */
  public AlgorithmParameterSpec getMGFParameters() {
    return mgfSpec;
  }

  /**
   * Returns the salt length in bits.
   *
   * @return the salt length.
   */
  public int getSaltLength() {
    return saltLen;
  }

  /**
   * Returns the value for the trailer field, i.e. bc in PKCS#1 v2.1.
   *
   * @return the value for the trailer field, i.e. bc in PKCS#1 v2.1.
   * @since 1.5
   */
  public int getTrailerField() {
    return trailerField;
  }
}
